This invention relates to walkways for platforms on offshore marine structures and more particularly to walkways between adjacent platforms which move relative to each other, particularly in a vertical direction.
In an offshore marine structure, such as an offshore production facility, a moon pool is oftentimes provided in the production deck or platform in which a plurality of production wellhead assemblies are mounted. Each of the production wellhead assemblies has a platform on which workmen may be supported while servicing a wellhead such as the valves and actuators on the wellhead. Workmen must walk or travel between adjacent platforms in order to have access to the associated wellhead assembly for various reasons, such as installations, maintenance, replacement, repair, and operations, for example. Heretofore it has been common to provide metal planks between adjacent platforms which would be removed in the event of storms, high seas, or when not in use. Substantial relative movement, particularly vertical movement, occurs between adjacent platforms which movement, for example, may be as much as 4 or 5 feet between adjacent platforms. The platform which forms a production deck of an offshore facility may have even greater vertical movement relative to the wellhead platforms, such as 10 to 15 feet resulting from high seas or storms. Relative horizontal movement also occurs between adjacent platforms and walkways must be capable of compensating for such relative movement between adjacent platforms which are connected by walkways.
It is desirable that walkways for offshore marine structures be provided between adjacent platforms or supporting surfaces with the walkways being adapted to compensate for relative movements between the adjacent platforms and provide safety for workmen to travel over between the adjacent platforms.
U.S. Pat. No. 4,011,615 issued Mar. 15, 1977, shows a gangway for connection between a ship and a fixed structure such as an offshore platform. The gangway in one embodiment shows a pair of box-type sections arranged for sliding movement relative to each other with shock absorbers to control the speed of the relative movement to limit the rate at which tension or compression is applied. U.S. Pat. No. 4,011,615 does not show any support rods and associated bearings for supporting the sections for sliding movement to minimize the frictional contact between the slidable sections and to provide accurate guiding of the slidable section upon relative movement.
U.S. Pat. No. 6,067,926 dated May 30, 2000, discloses a portable ramp extending between a dock and a boat with a pair of telescoping slidable sections. The slidable sections are provided for mounting of the ramp onto the boat and dock. However, during operation after mounting the ramp, the slidable connections are connected to each other so that relative movement is not provided.
The present invention is directed to a ramp or walkway particularly adapted for use between platforms on an offshore facility in which relative vertical and movement of substantial distances, such as 5 to 15 feet, may be obtained between adjacent platforms over which walkways workmen travel between adjacent structures in a safe manner. The walkway is formed of two sliding walkway sections which are mounted between the adjacent platforms and, upon relative movement between the adjacent platforms, the walkway sections slide relative to each other to compensate for the relative movement. The walkway may extend between a pair of adjacent platforms, for example, such as wellhead platforms provided adjacent wellhead assemblies mounted in a moon pool in the production deck of an offshore facility. The walkway may extend between a platform on the production deck and a wellhead platform so that workmen from the production deck may have access to the wellheads along a safe walkway. The walkways are designed to remain in place in the event of storms or high seas.
The present invention includes two walkway embodiments, one embodiment for extending between a pair of wellhead platforms, and the other embodiment for extending between a wellhead platform and an upper platform on the production deck. Each sliding walkway section has a walkway floor or deck on which a workman is supported for walking between adjacent platforms. The walkway floor on one sliding section is mounted over a walkway floor for the other sliding section and an extending end portion on one walkway section overlaps an extending end portion on the other walkway section. Relative vertical and horizontal movements frequently occur between adjacent platforms and the walkway of the invention is effective to compensate for such movements.
The pair of sliding walkway sections are connected to the adjacent platforms by a removable connection comprising interfitting connecting members on each sliding section and an adjacent platform for removably connecting the sliding sections to the pair of selected platforms. The interfitting connecting members may comprise a tubular member secured to an outer end of each sliding section and a support rod removably connected to an adjacent platform received within the tubular member. The tubular member preferably has a diameter substantially greater, such as five times greater, than the diameter of the support rod so that a substantial relative movement of 5 inches, for example, may be provided between each rod and the receiving tubular member on the sliding walkway section.
An object of the invention is to provide a walkway between adjacent platforms of an offshore facility which effectively compensates for relative vertical and horizontal movements between the adjacent platforms.
A further object of the invention is to provide such a walkway which includes a pair of slidable walkway sections having floors which overlap each other and with each section having an outwardly extending end removably connected to an adjacent platform.
Another object of the invention is to provide a walkway having a pair of slidable walkway sections which slide relative to each other under minimal frictional forces.